Thermoelectric energy conversion devices employ electrons for energy transfer. Such devices can operate in a refrigeration mode, e.g., by applying a current to transfer heat away from a cooling target, or can operate in a power generation mode, e.g. by using a load circuit to generate power from the temperature difference between two thermal reservoirs. However, phonon heat conduction (i.e., heat conduction due to vibration motion of the atoms in the thermoelectric material) typically reduces the efficiency of such devices, because it tends to transfer additional heat detrimentally from the heat source to the cold reservoir in power generation mode or transfer heat from the hot reservoir to the cooling object in refrigeration mode.
Attempts have been made to decouple electron and phonon thermal energy transport by incorporating a gap in the device that prevents phonon transfer, for example in vacuum thermionic devices and electron tunneling refrigerators. Electron thermionic emission, however, is limited by the work function of available materials. The electron tunneling refrigerators relies on a thin enough (on the scale of angstroms) vacuum gap to allow thermal energy transfer through quantum mechanical tunneling of electrons across the gap. The total energy transport in these devices is limited by the amount of current that can be transferred via quantum tunneling. Further, it is difficult to manufacture and maintain the precision gap required for the tunneling effect to operate.
Others have tried to minimize phonon transfer in electron tunneling devices by separating two materials by angstrom scale features which contact the separated materials but have minimal surface contact. Such devices thus still have some phonon energy transfer and are still limited as above by the amount of current that can be transferred via quantum tunneling.
Therefore, there is a need for efficient thermoelectric devices which have increased efficiency, and which can overcome the problems discussed above.